Process for the production of 2-aryl-2H-benzotriazoles

A process for the production of 2-aryl-2H-benzotriazoles of the formula I ##STR7## wherein R.sub.1 is hydrogen or chlorine,

• R.sub.2 is hydrogen, chlorine, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, carboxy or --SO.sub.3 H,
• R.sub.3 is alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having 1 to 8 carbon atoms, cycloalkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, chlorine, carboxyethyl or phenylalkyl of 7 to 9 carbon atoms,
• R.sub.4 is hydrogen, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, chlorine or hydroxyl, and
• R.sub.5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or phenylalkyl of 7 to 9 carbon atoms,
• which comprises
• reducing and cyclizing the corresponding o-nitroazobenzene ##STR8## with hydrogen at a temperature in the range of from about 20.degree. C. to about 100.degree. C. and at a pressure in the range of from about 15 psia (1.05 kg/cm.sup.2, 1 atmosphere) to about 1000 psia (70 kg/cm.sup.2, 66 atmospheres) while mixed in an alkaline organic solvent mixture comprising an organic amine in a concentration of at least 0.1 mole of amine per mole of o-nitroazobenzene in the presence of hydrogenation catalyst selected from the group consisting of the noble metals of Group VIII of the Periodic Table with the proviso that the hydrogenation catalyst cannot be palladium-on-asbestos, and with the proviso that, when R.sub.1, R.sub.2, R.sub.3, R.sub.4 or R.sub.5 is chlorine, the hydrogenation catalyst cannot be palladium,
• separating the catalyst which is suitable for recycle, and recovering the desired 2-aryl-2H-benzotriazole.